1. Field of the Invention
The present invention is directed to voltage regulation in multi-voltage supply applications, and in particular, for peripheral devices such as memory systems.
2. Description of the Related Art
Advances in integrated circuit (IC) technology often relate to decreasing the size and operating voltages of devices used to fabricate circuitry. Lower power devices generally translate into lower costs due to decreases in circuit size and power consumption. Currently, low-voltage integrated circuits having transistors operating in the three-volt range and lower are highly desirable. The three-volt ICs are gradually replacing the standard five-volt ICs due to their higher speed and higher integration densities. Moreover, the three-volt ICs consume less power than the traditional five-volt ICs. In battery operated devices, such as portable telephones and lap-top computers, low-voltage integrated circuits allow the devices to operate proportionally longer than devices requiring higher voltage for operation.
Improvements in processing technology have led to smaller transistor device sizes. This in turn has led to lower power supply requirements in each successive generation of transistor technology. For example, a 0.25 micron process device operates on a voltage of approximately 2.5 volts, a 0.18 micron process uses a 1.8v (+/−10%) supply, a 0.15 micron process will use a 1.5 (+/−10%) volt supply, 0.13 micron technology a 1.2v (+/−10%) supply, and so on.
The lower power requirements of newer semiconductor processes are not always compatible with legacy host devices. For example, older hosts may supply 5 or 3 volts to a memory system requiring only 3 or 1.8 volts, respectively. Computer peripheral devices must therefore be designed to accommodate connections from both 3.3 volt host supplies as well as older, higher voltage supplies. Devices constructed with newer technologies therefore allow for the possibility that the host device in which they are used will supply a higher voltage used with legacy products. Hence power level detection and voltage regulation techniques are used to provide the correct voltage to the memory device.
One such peripheral device which must make such adjustments is non-volatile memory which might be used in cellular telephones, digital cameras, personal digital assistants, mobile computing devices, non-mobile computing devices, audio and video players and other appliances. Electrical Erasable Programmable Read Only Memory (EEPROM) and flash memory are among the most popular non-volatile semiconductor memory types.
Non-volatile memory may be coupled to a host device in a number of ways. Peripheral adapters include integrated adapters coupled directly to a computers system bus and power supply, and peripherals adapted to connect to any of a number of industry standard external system connections, such as Universal Serial Bus or the IEEE 1394 Standard. A common interface used to couple non-volatile memory to such devices is the Universal Serial Bus interface. Many current USB devices are designed to operate at 3 volt, but may receive a supply in the 3 volt or 5 volt range from legacy devices.
Generally, in order to couple peripherals manufactured with newer process technologies to legacy or hosts providing higher-supply voltages, step-down voltage regulators are used. Where the regulator is integrated with the peripheral, it would be desirable to manufacture the regulator using the same process technology as that used to manufacture devices in the peripheral. Generally, however, this is not possible, since the input load to the regulator can damage lower voltage devices.
Co-pending application Ser. No. 10/633,110 discloses a voltage regulator which regulates a 5 volt supply to a 3 volt output with 3 volt devices. The devices are protected by a protection circuit within the device, allowing the device to operate with an input voltage greater than the operating level of the devices without damaging the devices.
The present invention provides an alternative implementation of a voltage regulator wherein devices having an operating range lower than the potential input voltages are used in the voltage regulator.